House Republicans are facing a last-minute uprising against Speaker John Boehner's budget deal, as dozens of GOP lawmakers are telling leadership they might vote against the package because of changes to crop insurance programs, and other concerns.

Senior GOP lawmakers estimate that between 60 and 120 Republicans will vote for the package as is, leaving Democrats to supply the vast majority of votes, though the vote count is fluid at this time. Aides in both parties expect the bill to pass, but the number of GOP defections is a notable rebuke to Boehner and other top Republicans.

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GOP leaders are trying to fix the crop insurance problem, but it isn't the only problem. Many hardline House conservatives – including members of the Freedom Caucus — will vote against the measure because of concerns about the process by which the bill was written. The package was crafted during weeks of secret talks between Boehner, Senate Majority Leader Mitch McConnell (R-Ky.), President Barack Obama, and Democratic leaders on Capitol Hill. Conservatives complain that they were not consulted on the measure, that no committee hearings were held, and that members are being presented with an up-or-down, take-it-or-leave-it vote.

Furthermore, Republicans are wrangling with the Congressional Budget Office over how the bill's cost is calculated. CBO estimates that the package will increase the deficit by $14 billion, although that assessment is questionable. House aides said the bill may be revised to fix an “error” that led CBO to overestimate the cost of the package by as much as $10 billion.

But it was the crop insurance issue that was causing GOP and Democratic leaders the biggest headache on Tuesday night. In a surprising move, Rules Committee Chairman Pete Sessions (R-Texas), whose committee sets the parameters for floor debate, bucked his own leadership by saying he wouldn’t mark up the bill until he has more information on the changes to the federal crop insurance program and the budgetary score.

The legislation mandates that when the Department of Agriculture negotiates with crop insurers, the companies must accept a lower rate of return. Crop insurers have complained loudly to lawmakers, who are in turn complaining to party leaders. CBO estimates the provision will bring in $3 billion in additional revenue over the next decade.

Agriculture Committee Chairman Mike Conaway (R-Texas) said he was "a no right now” on the budget deal because of this issue. Rep. Collin Peterson (D-Minn.), ranking member of the panel, is also opposed.